(1) Field of the Invention
The present invention generally relates to an ink jet printing head and a method of producing the ink jet printing head. More particularly, the present invention relates to an ink jet printing head having a nozzle plate with a plurality of nozzles for discharging ink by stressing the ink through actuation of piezoelectric elements, and to a method of producing the ink jet printing head.
(2) Description of the Related Art
An ink jet printing head is capable of printing an image on plain recording paper without contacting the printing head with the recording paper. The ink jet printing method is a simple printing process that can be performed, and it can be easily applied to color image printing. A special attention has been paid to the ink jet printing method.
In recent years, an on-demand ink jet printer system in which ink is forced out to the recording paper by an ink jet printing head in accordance with a print signal has become popular. There are two types of the on-demand ink jet printer systems: a thermal jet type and a piezoelectric actuation type. Concerning the two types of the on-demand ink jet printer systems, the disclosure of U.S. patent application Ser. No. 517,719 filed on Aug. 21, 1995, which is assigned to the assignee of the present invention, is herein incorporated by reference.
Generally, the ink jet printing head includes a nozzle plate with a plurality of nozzles for discharging ink to the recording paper, and an energy generating part for generating energy in accordance with a print signal. The energy generated by the energy generating part stresses the ink within the ink jet printing head so that the ink is discharged from the nozzles. It is known that the application of a surface treatment to the nozzle plate to form a water-repellent layer on the outer surface of the nozzle plate is effective to stabilize a discharge of ink from the nozzle.
More specifically, in order to provide a stable, constant discharge of ink from the nozzle of the ink jet printing head, it is necessary to efficiently transmit the energy from the energy generating part to the ink. If no water-repellent layer on the nozzle plate is formed, the ink coming out from the nozzle tends to stick to the outer surface of the nozzle plate adjacent to the nozzle when it is discharged. The water-repellent layer on the outer surface of the nozzle plate helps provide an efficient transmission of the energy to the ink.
Various surface treatments for the ink jet printing head which are intended to provide a stable, constant discharge of ink from the nozzle are known.
Japanese Laid-Open Patent Application No. 55-65564 teaches a water-repellent surface treatment applied to an orifice-surrounding surface of a printing head. For the water-repellent surface treatment, a silicon-containing water-repellent agent or a fluorine-containing water-repellent agent is applied to the orifice-surrounding surface to form a water-repellent layer thereon.
Japanese Laid-Open Patent Application No. 56-89569 teaches a water-repellent surface treatment applied to an orifice-surrounding surface of a printing head. For the surface treatment, a special fluorine-containing organic silane compound is used to form a water-repellent surface thereon.
Japanese Laid-Open Patent Application No. 64-87359 teaches a plasma-polymerized high-molecular layer formed on an orifice-surrounding end surface of an ink jet printing head. For such a surface treatment, a fluorine-containing compound or a silicon-containing compound is used to form the layer thereon.
Japanese Laid-Open Patent Application No. 2-39944 teaches a water-repellent surface treatment applied to an orifice-surrounding surface of an ink jet printing head. For the surface treatment, a special fluorine-silicon-containing compound is used.
Japanese Laid-Open Patent Application No. 63-3963 teaches a water-repellent layer formed on a nozzle plate of an ink jet printing head. The water-repellent layer is formed through fluorine-containing high-molecular compound eutectoid plating.
Japanese Laid-Open Patent Application No. 4-294145 teaches a water-repellent layer formed on a nozzle-surrounding surface of an ink jet printing head. The water-repellent layer is formed through fluorine-containing high-molecular compound eutectoid plating.
The conventional methods of forming the surface treatment layer using the above-mentioned surface treatments may be classified into two categories: the forming of the surface treatment layer by vacuum evaporation or the like after the forming of the nozzles in the nozzle plate is completed; and the forming of the nozzles in the nozzle plate by punching or the like after the forming of the surface treatment layer is completed.
FIG. 1 shows a surface treated nozzle plate 102 in the case of a conventional ink jet printing head which is produced by using the latter method (the punching to form a nozzle 103 in the nozzle plate 102 is performed after the surface treatment layer 101 is formed).
FIG. 2 shows another surface treated nozzle plate 101 in the case of another conventional ink jet printing head which is produced by using the former method (the surface treatment layer 101 is formed after the nozzle 103 in the nozzle plate 102 is formed).
In both cases, the surface treatment layer 101 has, as shown in FIGS. 1 and 2, an opening whose diameter at a peripheral edge 101a of the surface treatment layer 101 is greater than or equal to an inside diameter of the nozzle 103 at a peripheral edge 102a of the nozzle plate 102. Since the diameter of the opening of the surface treatment layer 101 is greater than or equal to the diameter of the nozzle 103 at the peripheral edge 102a of the nozzle plate 102, the ink coming out from the nozzle 103 tends to stick to the outer surface of the nozzle plate 102 adjacent to the nozzle 103 when it is discharged. Therefore, it is difficult for the conventional ink jet printing head to efficiently transmit the energy from the energy generating part to the ink when it is discharged.
Accordingly, there is a problem in that the efficiency of the discharging of ink of the conventional ink jet printing head is lowered, and that the discharging characteristic of the conventional ink jet printing head becomes unstable. Further, it is difficult for the conventional ink jet printing head to provide a stable, constant discharge of ink because of the relatively great inside diameter of the opening of the surface treatment layer 101.